The processes of stem cell specification, organ development and tissue formation are common to all complex multicellular organisms. Arabidopsis thaliana is an excellent model system in which to study these processes because the stem cell populations are clearly defined and continuously generate new organs and tissues. Studies by our laboratory and others have found interesting parallels between plant and animal systems, including the presence of stem-cell niches, the involvement of receptor kinase proteins and most recently, the role of cell polarity. Two protein phosphatase type 2C proteins, POL and PLL1, were recently identified in Arabidopsis as being involved in both meristem regulation and the determination of cellular polarity. POL and PLL1 mutants and overexpressors have been well characterized at the phenotypic level. Little is known, however, about the cellular roles of POL and PLL1 and how these proteins are regulated. Bioinformatics and localization studies in Saccharomyces cerevisiae suggest that POL and PLL1 are N-myristoylated and palmitoylated, which may regulate their localization and/or activity. The first two aims of this proposed research are to determine where POL and PLL1 are localized in the cell and how their activities are regulated. Also, since only a few components of the pathways in which POL and PLL1 function have been identified, the third aim of this proposal is to isolate cellular components that interact with POL and PLL1. The overall goal of this proposal is to obtain a better understanding of the pathways POL and PLL1 are regulated by and the pathways they are regulating. Understanding these pathways should help us gain further knowledge of stem cell specification and differentiation, which could lead to advancements in the fields of medicine and agriculture. [unreadable] [unreadable] [unreadable]